The Weather of February 2018

With the persistence of an intense winter monsoon during the early part of the month, the weather of February 2018 was overall cooler than usual. The monthly mean temperature of 16.0 degrees was 0.8 degree below the normal figure of 16.8 degrees. It was also relatively dry with only 4.5 millimetres of rainfall recorded in the month, less than 10 percent of the February normal of 54.4 millimetres. The accumulated rainfall for the first two months of the year was 66.7 millimetres, about 15 percent below the normal figure of 78.9 millimetres for the same period.

An intense winter monsoon that started to affect the south China coastal areas in late January continued its dominance into the early part of February. Cold weather persisted till 8 February, with the lowest temperature of the month, 6.8 degrees, recorded at the Hong Kong Observatory on 1 February and frost being reported in places over the territory during the period as well. Following the arrival of a cold but dry continental airstream on 5 February, the initially cloudy conditions gave way to sunny skies the next day and daytime relative humidity dropped to 40 percent or below on 5 – 7 February.

Apart from a couple of cloudy interludes on 7 and 9 February, generally fine weather persisted till 13 February. Temperatures started to climb during the period as the winter monsoon moderated, but a replenishment of northerly winds soon brought another cold snap on 12 February. Approaching the Chinese New Year festive period, the winter monsoon finally loosened its grip and moister air of maritime origin started to move in towards the south China coast. This led to increased cloudiness at first but as temperatures rose, a sunny and mild day greeted the first day of Chinese New Year on 16 February.

After some morning fog on 17 February, a freshening easterly airstream brought cloudy and cooler weather to Hong Kong. As the easterly winds moderated, a warm maritime airstream returned to the coastal areas of Guangdong on 19 February and temperatures over most parts of the territory rose to 25 degrees or above on 20 February. Meanwhile, generally cloudy conditions persisted and with a replenishment of the winter monsoon coming down the coast of southeastern China, the weather in Hong Kong turned cooler again on 21 February. This was followed by the setting in of a fresh northerly airstream that brought overcast skies with rain patches and led to temperatures falling further over the next couple of days.

As the winter monsoon subsided, two days of relatively mild and brighter weather followed on 24 and 25 February. Under the influence of a fresh easterly airstream, the weather then turned generally cloudy and cooler again the next day. As the easterly winds moderated, it became warm with sunny periods on 27-28 February. Temperatures at the Hong Kong Observatory climbed to the month’s highest of 26.2 degrees on the last day of the month.

Frost reported at Fanling on 6 February 2018

(Photo courtesy of Miss Kwok (left) and Mr. Yip (right))

One tropical cyclone occurred over the South China Sea and the western North Pacific in the month.

Details of issuance and cancellation of various warnings/signals
in the month are summarized in Tables 1.1 to 1.4. Monthly meteorological
figures and departures from normal for February are tabulated in Table 2.

Warnings and Signals issued in February 2018

Table 1.1 Strong Monsoon Signal

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

31 / 1

1600

1 / 2

0745

Table 1.2 Fire Danger Warnings

Colour

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

Yellow

1 / 2

0600

3 / 2

0600

Red

3 / 2

0600

7 / 2

0600

Yellow

7 / 2

0600

8 / 2

1900

Yellow

11 / 2

0600

11 / 2

2045

Red

12 / 2

0600

12 / 2

2230

Yellow

14 / 2

0720

14 / 2

2130

Table 1.3 Frost Warning

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

3 / 2

1930

4 / 2

0745

4 / 2

1630

5 / 2

1130

5 / 2

1630

6 / 2

0915

Table 1.4 Cold Weather Warning

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

28 / 1

1200

8 / 2

1115

10 / 2

1620

13 / 2

0955

Table 2 Figures and Departures from Normal - February 2018

Meteorological Element

Figure of the Month

Departure from Normal*

Mean Daily Maximum Air Temperature

18.7 degrees C

0.2 degree below normal

Mean Air Temperature

16.0 degrees C

0.8 degree below normal

Mean Daily Minimum Air Temperature

13.9 degrees C

1.1 degrees below normal

Mean Dew Point Temperature

10.4 degrees C

2.6 degrees below normal

Mean Relative Humidity

70 %

10 % below normal

Mean Cloud Amount

73 %

1 % below normal

Total Rainfall

4.5 mm

49.9 mm below normal

Number of hours of Reduced VisibilityΔ

49 hours

82.3 hours below normal§

Total Bright Sunshine Duration

108.7 hours

14.5 hours above normal

Mean Daily Global Solar Radiation

11.50 Megajoule / square metre

2.11 Megajoule above normal

Total Evaporation

63.9 mm

4.0 mm above normal

Remarks :

All measurements were made at the Hong Kong Observatory except sunshine,
solar radiation and evaporation which were recorded at King's Park
Meteorological Station and visibility which was observed at the Hong
Kong International Airport.

Δ

The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend.
Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway.

* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility

§ Departure from mean value between 1997 and 2017

Remarks :

Extremely high: above 95th percentile
Above normal: between 75th and 95th percentile
Normal: between 25th and 75th percentile
Below normal: between 5th and 25th percentile
Extremely low: below 5th percentile
Percentile and 5-day running average values are
computed based on the data from 1981 to 2010